update travis to test julia v1.5

Author: ccoffrin

.travis.yml

@@ -4,15 +4,15 @@ os:
   - osx
 julia:
   - 1.0
-  - 1.4
+  - 1.5
   - nightly
 codecov: true
 jobs:
   allow_failures:
     - julia: nightly
   include:
     - stage: "Documentation"
-      julia: 1.4
+      julia: 1.0
       os: linux
       script:
         - julia --project=docs/ -e 'using Pkg; Pkg.instantiate(); Pkg.develop(PackageSpec(path=pwd()))'